KR101160214B1 - Spark plug location for split-cycle engine - Google Patents

Abstract

The split-cycle engine includes individual compression and expansion cylinders connected by cross passages. Cross compression and expansion valves define a pressure chamber that stores the pressurized gas in the cross passages regularly before delivery into the expansion cylinder. One or more ignition sources, such as spark plugs, are located in the expansion cylinder to facilitate rapid combustion after ignition and are located far enough from the cross-expansion valve (s) to prevent the incorporation of burning gas. Prevents the combusting gases from reaching the crossover expansion valves prior to substantially closing.

Description

Location of spark plugs for split-cycle engines {SPARK PLUG LOCATION FOR SPLIT-CYCLE ENGINE}

The present invention relates to an internal combustion engine. More specifically, the present invention is directed to placing an ignition source inside an expansion cylinder of a split-cycle engine to prevent the injection of air / fuel mixture that is combusted into one or more cross-aisle expansion valve ports prior to the expansion valve closing time. It is about.

This application takes precedence over US Provisional Patent Application No. 60 / 963,742, filed with US Patent Office on August 7, 2007.

For clarity, the following definitions are provided for the term split-cycle engine so as to be applicable to the engines disclosed in the prior art and referenced in the present application.

The split-cycle engine described in the present invention,

A crankshaft rotatable about a crankshaft axis;

A compression piston slidably received in the compression cylinder and operably connected to the crankshaft to reciprocate through a suction stroke and a compression stroke during one rotation of the crankshaft;

An expansion (power) piston slidably received in an expansion cylinder and operably connected to the crankshaft for reciprocating through an expansion stroke and an exhaust stroke during one rotation of the crankshaft; And

And a crossover passage that interconnects the compression and expansion cylinders and includes a crossover compression (XovrC) valve and a crossover expansion (XovrE) valve defining a pressure chamber.

US Patent No. 6,543,225, issued to Carmelo J. Scuderi on April 8, 2003, includes extensive discussion of split-cycle engines and similar types of engines. The patent also discloses detailed descriptions of the engine corresponding to the conventional version, in which the invention comprises a further development of the engine.

Referring to FIG. 1, an exemplary embodiment of the split-cycle engine concept of the prior art is generally shown by reference numeral 10. The split-cycle engine 10 replaces two adjacent cylinders of a conventional four stroke engine with one compression cylinder 12 and one expansion cylinder 14. These two cylinders 12, 14 perform their respective functions once per revolution of the crankshaft 16. The intake air and fuel charge is sucked into the compression cylinder 12 through intake valves 18 of a typical poppet type. The compression cylinder piston 20 pressurizes the charge through the crossover passage 22 and moves the charge through the crossover passage 22 which acts as the suction passage for the expansion cylinder 14.

A check type XovrC valve 24 is used in the cross passage inlet to prevent backflow from the cross passage 22 to the compression cylinder 12. The XovrE valve 26 at the outlet of the crossover passage 22 regulates the flow of pressurized suction charge, so that immediately after the expansion piston 30 reaches its top dead center TDC. All of this charge is introduced into the expansion cylinder 14. The spark plug 28 is ignited immediately after the suction charge flows into the expansion cylinder, and the resulting combustion moves the expansion cylinder piston 30 down to the bottom dead center BDC. Exhaust gases are pumped out of the expansion cylinder via poppet exhaust valves 32.

In the split-cycle engine concept, the geometric engine parameters of the compression and expansion cylinders (ie bore, stroke, connecting rod length, compression ratio, etc.) are generally independent of each other. For example, the crank throws 34, 36 of each cylinder may have different radii, and the top dead center of the expansion cylinder piston 30 which takes precedence over the top dead center (TDC) of the compression cylinder piston 20. The phases can be different from each other. The independence allows the split-cycle engine to achieve potentially higher efficiency levels and greater torque than typical four-stroke engines.

The cross expansion (XovrE) valve 26 takes only a short time (about 30 degrees crank angle) to discharge the pressurized air / fuel mixture into the expansion cylinder before completion of the compression cylinder piston stroke, so that the cross expansion Closure of the valve occurs after ignition of the air / fuel charge. An extended valve life is required to prevent the fuel mixture that is combusted without shortening the valve closing time from being injected into the crossover expansion valve.

It is an object of the present invention to provide a split-cycle engine capable of preventing the injection of an air / fuel mixture that is combusted into one or more cross passage expansion valve ports prior to the expansion valve closing time.

In a split-cycle engine according to the invention, the spark plug or plugs are located in the expansion cylinder at a "safety distance" from the crossover expansion (XovrE) valve (s) to ignite prior to the substantial closure of the crossover expansion valve. The mixture burning from the point will not reach the valve. From the above, as well as other considerations for the location of the spark plug of conventional engines, it is also required to consider the design process so that the speed of flame is within the range of engine speeds.

The engine according to the invention comprises a crankshaft rotatable about a crankshaft axis;

A compression piston slidably received in the compression cylinder and operably connected to the crankshaft to reciprocate through a suction stroke and a compression stroke during one rotation of the crankshaft;

An expansion piston slidably received in an expansion cylinder and operably connected to the crankshaft to reciprocate through an expansion stroke and an exhaust stroke during one rotation of the crankshaft;

A crossover passage interconnecting the compression and expansion cylinders and including a crossover compression (XovrC) valve and a crossover expansion (XovrE) valve defining a pressure chamber; And

A cross-expansion valve port for closing one end of the expansion cylinder and seating the cross-expansion valve, and an ignition source center spaced from the nearest peripheral edge of the cross-expansion valve port to provide air / fuel at a predetermined ignition point in the expansion cylinder A cylinder head having an ignition source for generating a flame front of the gases that ignite and combust the mixture,

Wherein the ignition source center is located at a distance greater than the closest peripheral edge of the cross-expansion valve port at least as determined by a "safety distance" such that at least a portion of engine drive speeds the gases burned prior to the substantial closure of the valve Prevent progression into the cross-expansion valve port, wherein the safety distance " S "

S (millimeters) = burn rate (millimeters / crank angle) × crank angle from ignition to cross expansion valve closure,

Can be represented by

Additional aspects,

The ignition source center is located far enough from the cylinder wall to prevent cooling and quenching of the flame after ignition, too long to extend the combustion time of the charge and to cause self-ignition outside the flame front, so far from the cylinder wall. It may include not located far.

The center of the ignition source may comprise at least 12 mm from the nearest peripheral edge of the exhaust valve in the cylinder head to allow space for sufficient cooling of the cylinder wall adjacent to the ignition source.

The split-cycle engine according to the present invention thus constructed can locate an ignition source inside the expansion cylinder to prevent the injection of air / fuel mixtures that are combusted into one or more cross-aisle expansion valve ports prior to the expansion valve closing time. .

The above and other aspects and advantages of the present invention will become more fully understood from the following detailed description of the invention in conjunction with the accompanying drawings.
1 is a cross-sectional view of a prior art split-cycle engine associated with the engine of the present invention.
2 is a cross-sectional view illustrating a split-cycle engine according to an embodiment of the present invention.
3 is a plan view taken along line 3-3 of FIG. 2 with fuel injectors applied;
4 is a bottom view of the cylinder head showing the relative positions and principal dimensions of the valves and the ignition sources.
FIG. 5 depicts the passage of flame into the cross-expansion valve seat at 25 degree ATDC when the valve is closed.
FIG. 6 is a line graph showing engine safety versus predicted safety distance between the ignition source center and the nearest peripheral edge of the cross compression valve port.
FIG. 7 is a two-dimensional plot showing the progress of a flame when ignited at 14 degrees ATDC at 23 degrees ATDC at 1400 rpm.

2 and 3, reference numeral 50 generally denotes a split-cycle engine according to an embodiment of the present invention. The engine 50 includes a crankshaft 52 rotatable clockwise about the crankshaft axis 54 as shown in the figure. The crankshaft 54 is connected to the connecting rods 60, 62, respectively, and includes crank throws 56, 58 that are adjacent, alternately angled, and behind.

The engine 50 also includes a cylinder block 64 defining a pair of adjacent cylinders, in particular the cylinders having one end of the cylinders closed by a cylinder head 70 opposite the crankshaft 52. Compression cylinder 66 and expansion cylinder 68.

The compression piston 72 is received in the compression cylinder 66 and is connected to the connecting rod 62 so that the piston can reciprocate between the top dead center (TDC) and bottom dead center (BDC) positions. The expansion piston 74 is received in the expansion cylinder 68 and is connected to the connecting rod 60 for similar top dead center / bottom dead center reciprocating movement.

In one embodiment, the cylinder head 70 provides a means for gas flow into and out of the cylinders 66 and 68 and for gas flow between the cylinders. In accordance with the order of the gas flow, the cylinder head includes a suction port 76 through which suction air is sucked into the compression cylinder 66, and compressed air (gas) moves from the compression cylinder 66 to the expansion cylinder 68 (at least). Double crossover passages 78, in which one passage is required, and an exhaust port 80 through which the gases used are discharged from the expansion cylinder. Each cross passage 78 also defines a pressure chamber 81 in which a gas is maintained at a constant pressure when the cross compression and expansion valves are closed.

The gas flow into the compression cylinder 66 is regulated by an inlet valve 82 of the poppet type that opens inward. Gas flow into and out of each crossover passage 78 is coupled to a pair of outwardly open poppet valves (ie crossover compression valves 84 at the inlet ends of the crossover passages and the outlet end of the crossover passages). By means of cross expansion valves 86). The exhaust gas flow out of the exhaust port 80 may be regulated by an inwardly open poppet type exhaust valve 88. The valves 82, 84, 86, and 88 can be driven in a suitable manner by mechanically actuated cams, various valve drive techniques, or the like.

With continued reference to FIGS. 2 and 3, the exemplary engine 50 also includes one or more spark plugs 90 or other ignition sources disposed at appropriate locations at the end of the expansion cylinder, and the expansion cylinder The mixed fuel and air charge in the ignition can be ignited and burned during the expansion stroke.

The engine also requires at least one fuel injector 92 that operates to inject fuel into the compressed air charge inside at least one (or both) of the cross passages 78 and the pressure chambers 81.

Referring to FIG. 4, one embodiment of a spark ignition (SI) split-cycle engine 50 is a cylinder with double cross expansion (XovrE) valves 96 seated in a cross expansion valve port 98. With a head face 94, the crossover expansion valves (not shown) open outwardly with respect to the expansion cylinder 68.

The cylinder head surface 94 also includes at least one exhaust valve 100 seated at the exhaust valve port 102 and a spark plug, incandescent plug, switch laser, or regulating means capable of sufficiently raising the temperature of the fuel / air. At least one ignition source 104 located at a specific location, such as a field, where the onset of combustion occurs. As discussed in more detail herein, the center 106 of each ignition source 104 is designated by the safety distance “S” (reference numeral 108) from the closest peripheral edge 110 of each cross-expansion valve port 98. ) The relative positions of the cross inflation valves 96, the exhaust valve 100 and the ignition sources 104 are important for the following reasons.

a) to guarantee excellent fuel mixing;

b) to promote proper charge movement in the cylinder;

c) to prevent flame from burning into said crossover passage;

d) to prevent self-ignition ("explosion") of the fuel air mixture before the flame reaches (explosion is an uncontrolled self-ignition phenomenon of pockets of unburned fuel and air, and generally To prevent spark-ignition of the engine); And

e) It is important to get combustion fast enough before the piston goes down too far.

Having a pair of ignition sources 104 has the advantage of increased combustion speed, and more importantly for the split-cycle engine 50, the use of a pair of ignition sources 104 Greater flexibility is provided in realizing a minimum safety distance 108 from the nearest peripheral edge 110 of the cross-expansion valve port 98. Because a single ignition source is usually located in the center of the cylinder to provide the same flame propagation path in all directions, thus providing a relatively faster combustion time compared to offset ignition sources. However, the centrally located ignition source is not ideal for the split-cycle engine 50, where the center of the centrally located ignition source is cross-expansion valve port 98 compared to the center 106 of the pair of ignition sources 104. This will tend to be closer than the nearest peripheral edge of, and therefore less likely to meet the minimum safety distance criterion compared to a pair of ignition sources. The pair of ignition sources 104 can be moved further away from the closest peripheral edge of the cylinder center and cross expansion valve port 98 while still achieving sufficiently fast combustion times.

There are three main variables that affect the selected position of the ignition sources 104 of the split-cycle engine 50.

Variable 1. Distance to Nearest Peripheral Edge 110 of Cross-Expansion Valve Ports 98

Referring to FIG. 5, in order to obtain combustion as close as possible to top dead center (TDC) in the split-cycle engine 50, ignition needs to occur before the cross-expansion valves 96 are closed. However, it is also important to prevent the flame 112 from moving inside the cross expansion valve ports 98 due to the durability and thermal efficiency losses of the cross expansion valve 96. Thus, in order to allow the valves to be substantially closed before the flame 112 reaches the cross inflation valves 96, the centers 106 of the ignition sources 104 are connected to the cross inflation valve ports 98. It needs to be located far enough from the nearest peripheral edge 110. Although the actual valve 96 closure occurs at 25 degrees after top dead center (ATDC), the actual closure is selected to occur at 23 degrees past the top dead center within the scope of safety of flame 112 penetration. FIG. 5 shows flame 112 reaching, penetrating and overlapping with valve 96 at 23 degree ATDC, but the flame reaches the nearest peripheral edge 110 of cross-expansion valve port 98. When the valve / seat clearance is less than 0.5 mm at 23 degrees ATDC is acceptable as above.

Variable 2. Distance to cylinder wall (68)

First, the ignition source 104 too close to the cylinder wall 68 can cause cooling and quenching of the flame and is not ideal for promoting combustion in the initial combustion phase.

Secondly, the ignition source 104 too far of any of the cylinder walls 68 will result in an extended combustion time until the flame reaches the unburned mixture. As a result of this, thermal efficiency is reduced and self-ignition of the unburned mixture due to the compression of the unburned mixture and the radiant heat transfer from the flame before the flame reaches the unburned mixture location ( Explosion).

For this first reason, the first and second ignition sources 104 are also typically located at least 20% of the cylinder bore diameter from the periphery of the cylinder bore 68. For this second reason, the single ignition source 104 should not be located more than 60% of the cylinder bore diameter from any portion of the cylinder wall region above the cylinder bore 68.

Variable 3. Distance to nearest peripheral edge of exhaust valve port 102

Sufficient cooling passages (not shown) are required in the cylinder head water jacket between the spark plug protrusion (not shown) and the exhaust port 102 gap. The minimum distance is usually determined by casting limits, such as the minimum possible mold wall thickness or the minimum sand core portion viable for forming the cooling jacket. The requirement generally requires a minimum of 12 mm between the center 106 of the ignition source 104 and the nearest peripheral edge of the exhaust valve port 102.

Referring to FIG. 6, a graph 114 is derived from the computational fluid dynamics (CFD) prediction results of combustion and the importance of variable 1 for the split-cycle engine 50 is described. Line 116 shows the engine speed (graph (the vertical axis of graph 114)) that the flame 112 traveled from the onset of ignition to the moment of closing of the cross-expansion valve 96 under full load conditions. The horizontal axis of Fig. 114). If the distance from the nearest peripheral edge 110 of the crossover expansion valve port 98 to the ignition source 104 is greater than the value indicated in line 116, the arrangement causes the crossover expansion valve 96 to close. The flame 112 can be prevented from penetrating into the cross inflation valve port 98 before, and the arrangement can be referred to as "safety distance S". If the distance is less than the value shown in line 116, the arrangement will cause flame penetration into the cross inflation valve port 98 before the cross inflation valve 96 is closed. Graph 114 also shows that the theoretical safety distance is about 19 mm (point 118) at 1400 rpm, flame speed 2.14 mm / degree, and 35 mm (point 120) at 4000 rpm, 5.74 mm / degree flame speed. Point 122 is the actual position of the ignition sources 104 modeled in the results of the CFD analysis that generated the graph 114. Point 122 represents a safety distance of 19.8 mm to enable optimal ignition for engine 50 at 1500 rpm.

The inclination of line 116 is the full load from the combustion speed at the speed of the engine (speed of flame 112 front) and the closing of the cross-expansion valve 96 at approximately 14-20 degrees ATDC to 25 degrees ATDC, respectively. All depend on the above time from the onset of ignition. In typical two-stroke and four-stroke combustion, the time possible until combustion progresses and completes decreases linearly with increasing engine speed, while the main combustion speed increases linearly with increasing engine speed. Thus, the two factors lead to an approximately constant angular period for complete combustion throughout the engine speed range. Based on the combustion prediction results of the CFD, in a single plane 1 mm below the cylinder head face 94 in the split-cycle engine 50, the combustion speed at 4000 rpm is approximately 2.5 times higher than the combustion speed at 1400 rpm, The burn rate was defined in mm / crank angle, so a distance of approximately 1.8 times greater than the safety distance required at 1400 rpm between the ignition source 104 and the cross-expansion valve 96 at 4000 rpm is required.

The discrepancy between 1.8 times the safety distance at 2.5 rpm and 2.5 times the combustion speed at 4000 rpm and 1400 rpm is probably due to several factors, most importantly the safety of the cross-expansion valve 96 from ignition (14 ATDC) at 1400 rpm. This is because the angular period up to the closing point 23 ATDC is longer (9 degrees crank angle). On the other hand, due to the ignition timing delayed by 17 degrees ATDC at 4000 rpm, the corresponding period at 4000 rpm corresponds to 6 degrees ATDC, so that the optimum ignition timing can prevent the flame from penetrating into the cross-expansion port 98. The estimate of is the earliest in the latter case. If it is impossible to physically obtain the required safety distance between the ignition source center 106 and the nearest peripheral edge of the cross-expansion valve port 98, the ignition is further delayed after the top dead center (TDC). And, as a result, the thermal efficiency of the engine will be compromised.

Referring to FIG. 7, the schematic flame path between the ignition source 104 and the closest peripheral edge 110 of the cross-expansion valve port 98 was deduced, indicating the combustion progression at 1400 rpm as the CFD contour line. The front part of the flame is taken with a 2000 ° K contour. According to the example of FIG. 7 showing a single central ignition, the 17 degree ATDC contour is approximated to a simple white ellipse 124, and combustion occurs before the crossover valve is closed at 25 degree ATDC. Proceed to 23 degree ATDC contour 126 reaching the nearest peripheral edge immediately. In FIG. 7, the calculated distance is approximately 19 mm and corresponds to the safety distance (point 118) at 1400 rpm shown in FIG.

Referring to FIG. 6, the combustion speeds in the direction of the cross-expansion valve 96 at 1400 rpm indicate the travel distance between the two positions at the two 2000 ° K flame fronts between each flame front at 1400 rpm. Can be calculated by dividing by time interval or angular increment. The combustion speeds at this roughly averaged 1400 rpm are 18 meters / second (m / s), or 2.14 mm / crank angle, and the corresponding parameters at 4000 rpm are 138 m / s, or 5.74 mm / crank angle. The latter values are nominally increased by 30% from the calculated parameters to compensate for the application of the bias of the air / fuel ratio as a result of the CFD calculation at 4000 rpm.

Combustion chamber arrangements for gasoline fuels of the split-cycle engine 50 (as shown in FIGS. 1 and 3), according to variable 1 the safety distance at 4000 rpm should be greater than 35 mm, and distances less than 35 mm lose thermal efficiency. Will cause them. At lower speeds the safety distance can be reduced, for example up to about 19 mm at 1400 rpm, and at intermediate speeds possibly with values proportional to 19 and 35 mm. For example, a design value of 19.8 mm of the distance between the center 106 location of the ignition source and the nearest peripheral edge 110 of the cross-expansion valve port 98 provides optimal ignition up to about 1500 rpm (FIG. 6). Point 122).

Larger safety distances allow for optimum ignition timing up to about 4000 rpm, with the ignition sources 104 having to move closer towards the exhaust valve 100 and the cross-expansion valves 96 from the ignition sources 104. You have to move more. Due to the limited size of the cylinder bore 68 and the size of the exhaust valves 100, a compromise must be made, and ignition arrangements that are very off center should be remembered in most cases of harm from rapid combustion and explosion. An advantage of insufficient safety distance, such as 19.8 mm, is that better combustion times will be maintained at partial load conditions where much lower combustion speeds are calculated as a natural result of throttle engine operation. However, in hybrid applications, more full load driving will be required, and as a result of this will probably require the safety distances as shown in FIG.

Assuming deeper knowledge of the combustion speed of the split-cycle engine 50, at full load driving conditions from 1400 to 4000 rpm, the nearest peripheral edge of the ignition source 106 and the cross-expansion valve ports 98 ( The estimated 19-35 mm safety distance between 110 is an absolute value applicable to all cylinder bore sizes for split-cycle engines operating on gasoline fuels. If higher laminar combustion speeds are used or if any means are found to increase the combustion speeds, such as increasing turbulence, the safety distances will change. Apart from the effectiveness of the CFD prediction, similar safety distances can be calculated for the diesel drive.

In summary, the safety distance "S" in any split-cycle engine can generally be specified by the following relationship.

S (mm) = burn rate (millimeter / crank angle (mm / CAD)) × crank angle from ignition to cross-expansion valve closure

More easily, S has a flame contour traveling distance of ~ 23 degrees from the ignition source in the driving speed range of the engine under full load conditions for the highest safety distance value selected according to the expected duty cycle of the engine. It can be calculated from the CFD result, which indicates that above the selected speed, the ignition will be delayed to prevent combustion into the cross-expansion valve port 98.

The above expression may be expressed in a similar manner using the combustion speed in m / s and the combustion time in seconds, as calculated by the engine speed and crank angle.

According to variable 2 both centers 106 of ignition sources 104 should be located about 20% of the bore diameter from the periphery of cylinder bore 68 and according to variable 3 both centers of ignition sources 104. The fields 106 should be located at least 12 mm from the nearest peripheral edge of the exhaust valve port 102.

Such an arrangement provides a combustion system that prevents combustion into the cross-expansion valve port 98 before the cross-expansion valve 96 is closed, and also prevents combustion and explosion of the entire contents of the cylinder 68. Achieve the best tradeoff in

While the invention has been described from reference to detailed embodiments, it will be understood that numerical changes may occur within the spirit and scope of the invention as described. Thus, it is intended that the invention not be limited to the embodiments described above, but may have any scope defined in the language of the following claims.

Claims (13)

A crankshaft rotatable about a crankshaft axis;
A compression piston slidably received in the compression cylinder and operably connected to the crankshaft to reciprocate through a suction stroke and a compression stroke during one rotation of the crankshaft;
An expansion piston slidably received in an expansion cylinder and operably connected to the crankshaft to reciprocate through an expansion stroke and an exhaust stroke during one rotation of the crankshaft;
Two cross expansion valve ports for respectively seating corresponding cross expansion valves;
Interconnect the compression and expansion cylinders, and include at least one of a cross compression (XovrC) valve and the two cross expansion (XovrE) valves, the cross compression (XovrC) valve and the two cross expansion (XovrE) valves. At least one of the valves comprises a cross passage defining a pressure chamber;
A cylinder head closing one end of the expansion cylinder and including the two cross expansion valve ports; And
Two ignition sources disposed within the expansion cylinder, each comprising an ignition source center, the two ignition sources operative to ignite an air / fuel mixture within the expansion cylinder to generate a flame front of the combusted gases;
In each of the two ignition source centers, the distance from each ignition source center to the nearest peripheral edge of the two crossover expansion valve ports is the closest peripheral edge of the two crossover expansion valve ports from the center of the expansion cylinder. Internal combustion engine, characterized in that greater than the distance to. The safety distance (S) of claim 1, wherein each of the two ignition source centers is located at least at a safety distance (S) from a closest peripheral edge of each of the two crossover expansion valve ports. Or an internal combustion engine characterized by more than that. The internal combustion engine according to claim 2, wherein the safety distance (S) is in a range of 19 mm to 35 mm. delete delete 2. The internal combustion engine of claim 1, wherein each of the two ignition source centers is sufficiently far from the cylinder wall to prevent cooling and quenching of the flame after ignition. 7. The internal combustion engine of claim 6, wherein each of the two ignition source centers is located no greater than 60% of the diameter of the expansion cylinder from any portion of the expansion cylinder wall adjacent the expansion cylinder closing end. 7. The internal combustion engine of claim 6, wherein each of the two ignition source centers is located at least 20% of the cylinder diameter from the expansion cylinder wall adjacent the expansion cylinder closing end. 2. The two sources of ignition according to claim 1, wherein the cylinder head includes an exhaust port for receiving an exhaust valve, the center of each of the two ignition sources being at least 12 mm from the nearest peripheral edge of the exhaust port. An internal combustion engine, allowing space for sufficient cooling of adjacent expansion cylinder walls. 2. The internal combustion engine of claim 1, wherein the cross compression valve opens outwardly from the compression cylinder and the two cross expansion valves open outwardly from the expansion cylinders. delete delete delete

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